1. Field of the Invention
In one aspect the invention relates to semiconductive, crosslinkable, thermoplastic compositions while in another aspect, the invention relates to the use of these compositions in a process to make semiconductive, crosslinked articles under ambient conditions and without the use of peroxides.
2. Description of the Related Art
Existing technologies for manufacturing crosslinked articles from thermoplastic compositions rely mostly on peroxide-based compounds. Depending whether the article being made is molded or extruded, the manufacturing methods differ. For example, for a molded article, typically, the crosslinkable, thermoplastic compositions are first shaped into a tape or a strip, fed into a rubber injection press for melt-shaping, and finally cured in a hot mold at about 175° C. for 5 to 15 minutes (depending on, among other things, the formulation of the composition and the thickness of the article). For an extruded cable, the crosslinkable, thermoplastic compositions are fed to an extruder and co-extruded along with the insulation compound on a metal conductor, then passed through a high temperature continuous vulcanization tube (CV) to induce cross-linking. In either case, the peroxide cure initiator can be pre-incorporated or admixed with the crosslinkable thermoplastic composition at any time in the process. Scorch, i.e., premature crosslinking, is a common problem of this technology.
In cable manufacture, the process is slow, primarily driven by the limitation in achieving adequate cure across the cable thickness, especially the inner semi-conductive shield. Other technology used in cable manufacture relies on moisture cure where the cable is immersed in a hot water or a sauna to induce cross-linking. In this case a severe limitation exists on moisture diffusion to the inner most layer of the cable, i.e. the conductor shield, thus requiring long cure times. Thus the limitations of current moisture cure techniques to small size cables.